This invention relates to pipe joints and more particularly to swivel joints between adjacent lengths of pipe which are interconnected to form a pipeline for carrying fluids, for example for conveying fluids at high pressure in oil exploration and related industries.
Oil pipelines associated with exploration drilling rigs commonly comprise a series of interconnected lengths of steel pipe each of which includes a male connecting piece at one end and a female connecting piece at the other end. The inlets and outlets to be connected by such pipelines can be at various positions relative to one another and it is not always possible or practical to provide rigid pipelines particularly suited to all applications.
Consequently, it has become established practice to provide pipelines comprising lengths of pipe of various configurations, including linear and elbow-shaped lengths, which are interconnected with one another by means of swivel joints whereby relative axial rotation of adjacent lengths of pipe can occur. Thus, one or more swivel joints, together with appropriately-shaped lengths of pipe, can be incorporated in a pipeline to enable connection between points at differing heights and angles.
Swivel joints between adjacent lengths of pipe commonly incorporate a series of circumferential tracks or raceways within the male and female connecting pieces which house ball bearings as the bearing thrust medium. Sealing of the two pipe lengths relative to one another is achieved by means of annular sealing rings axially compressed between adjacent internal, radially extending faces of the male and female connecting pieces.
Such arrangements have a number of disadvantages. The pipelines in question, once they have adopted a desired configuration between two points to be interconnected, remain substantially in that position. Thus, the swivel joints eventually adopt a substantially stationary position, and it is not good engineering practice to use ball bearings for stationary, high load thrust situations. The bearings, as well as the tracks, can become dented and distorted, while such swivel joints are difficult to repair due to ball bearings having to be extracted and re-inserted through small apertures in the connecting pieces.
Further, and perhaps of even more importance, the seals associated with such swivel joints are very prone to failure. As the thrust bearing wears, the degree of axial compression on the annular sealing rings can decrease until leakage can occur, often with catastrophic results.